Combustion systems using fuels in gaseous or liquid form typically feed such fuels into a burner through a fuel nozzle. Such fuel nozzles generally have a sharp bend towards the end of the fuel nozzle flow pathway. Conventional fuel nozzles typically have an uneven fuel flow distribution which is caused by a higher centrifugal force near the inner radius of the bend than near the outer radius. Greater fuel flow is experienced near the outer radius of the bend in the form of increased stagnation pressure. As a result, the flame extending from the fuel nozzle tip becomes asymmetrical.
The undesirable effects of uneven flow distribution can be seen in combustion systems employing conventional fuel nozzles containing sharp bends. For example, in gas turbine fuel burners the combustion liner on an inner surface tends to be over-heated at the fuel rich part of the combustion chamber, thereby shortening a life span of parts therein. Another example can be observed in coal-fired boilers where pulverized coal particles are carried by air. The uneven distribution of pulverized coal powder in the burner section creates an oxygen-rich region and an oxygen starved region in the produced flame. The presence of such regions causes combustion deficiencies in terms of black smoke and/or undesirable CO concentrations as well as accelerates wear of parts.
Conventional nozzle designs for use in combustion systems are described in U.S. Pat. Nos. 7,174,717, 7,171,813, 7,104,069, and 7,104,070 which are incorporated herein by reference as part of this background discussion.
There is a need for a satisfactory solution to the problem of uneven flow distribution.
Commonly owned U.S. Pat. Nos. 5,323,661 and 5,529,084 (each of which is incorporated herein by reference) describes rotation vane devices for performing a rotational transformation in a fluid flow similar to the principle of rotational transformation in a magnetic confinement system of plasmas, and explains an approach for determining a curvature of turning vanes in said rotation vane device in order to minimize turbulence experienced by a fluid moving through a smooth pipe bend.
The approach of U.S. Pat. Nos. 5,323,661 and 5,529,084 does not address, however, the issue of uneven fuel flow being injected into a combustion chamber from a fuel nozzle comprising a sharp or mitered bend.
In addition the above mentioned fuel nozzles do not provide a solution to the problems of low frequency acoustic resonance encountered at subsonic flow conditions in combustion systems.